Oral Food Processing for Digitally Constructed Complete Dentures Versus Conventional Complete Dentures.

Fourteen completely edentulous patients were participated in this study, their ages range from 50- 70 years. The participants were selected from Prosthodontics Department, Faculty of Dentistry, Mansoura University who are seeking for complete denture treatment. All participants will be completely edentulous for at least 6 months and have no previous experience with removable prosthesis. Subjects with temporomandibular joint disorders, head/neck injury, or with skeletal deformity were excluded from this study. All participants were Angel's class I maxillomandibular relation. Informed consent were written from each patient, and approval from the Faculty Ethical Committee will be obtained. The sample size was deter¬mined based on the number of chews for TOMASS test data from previous research. A computer software program (G*power, version 3.1.5, Kiel, Germany) was used for sample size calculation. 14 participants was detected with an effect size of 72%, 5% error probability, and 80% power.

Complete dentures construction:

At the first visit Direct intraoral scanning of both arches were performed with an intraoral scanner (TRIOS 3; 3Shape A/S). Cheek retractors were used to gently extend the movable soft tissues. The ridge crest were scanned first, followed by scans of the labial or buccal and palatal or lingual surfaces of the ridge. For the maxillary arch, the palate were additionally scanned. After establishing the overall contour in this manner, the remaining unscanned parts were scanned to finalize the complete arch scan. Subsequently, preliminary impressions were made with an irreversible hydrocolloid impression material.

At the second visit Definitive impressions will be made using auto-polymerizing acrylic resin custom tray. The tray will be traced using low fusing modeling green compound then zinc oxide eugenol impression will be taken. For the fabrication of conventional CDs, the record base will be fabricated with an auto-polymerizing acrylic resin. For the fabrication of digital CDs, the record base will be directly designed on the intraoral scan data by using a CAD software program (Dental System, v1.7.16.0; 3Shape A/S) and will be additively manufactured with a 3D-printing material (Next- Dent C&B; 3D Systems) and a 3D printer (NextDent 5100; 3D Systems). Following this, a wax occlusal rim were attached to the record base.

At the third visit Maxillo-mandibular relationship were recorded by using the record base and wax occlusal rim assembly with an occlusal relationship registration material for both groups, and appropriate artificial teeth will be selected. For the fabrication of digital CDs, the obtained inter-arch relationship were scanned with the intraoral scanner. Subsequently, the standard tessellation language (STL) files for both edentulous arches and the registered inter-arch relationship will be imported into a metrology software program (Geomagic Control X, v2018.0.1; 3D Systems). The maxillary portion in the STL file of the registered interarch relationship will be flipped normal, creating a new STL file, and the original maxillary edentulous STL file were superimposed over this new flipped file through a best-fit matching algorithm. The same procedure were followed with regard to the mandibular portion in the STL file of the registered inter-arch relationship. This procedure enabled accurate 3D orientation of the obtained intraoral scan data. Next, the border of the CDs will be set 1 mm shorter than the scan border within the CAD software program. The artificial teeth will be arranged virtually, and the trial dentures were additively manufactured with the3D-printing material (NextDent C&B; 3D Systems) and the 3D printer. For the conventional dentures the artificial teeth were arranged in the conventional manner.

At the fourth visit Trial dentures were evaluated in both groups. The procedure for preparing the definitive CDs were initiated after the participant had accepted the trial dentures. For the fabrication of digital CDs, the gingival portion and the artificial tooth portion were fabricated separately by using the 3D printer and 3D printing materials (NextDent Base and NextDent C&B; 3D Systems) and were subsequently attached to each other. Conventional CDs were fabricated by using flasking technique with long curing cycle.

At the fifth visit The predetermined CDs type were delivered and will be adjusted and follow up visits will be scheduled.

The participants were randomly allocated into two equal groups (7 per group). An independent examiner using a computer program, specifically Microsoft Excel, will carry out randomization process. The first group of 7 participants were received digital CDs. At 3 months after denture use, the TOMASS test were done. After 1 week washout period, the participants wearied the conventional CDs for an additional 3 months, then the TOMASS test will be repeated. The second group of 7 patients will initially receive conventional CDs. At three months after denture use, the TOMASS test will be done. Then after 1 week washout period the participants will receive the digital CDs, and the test will be repeated after an additional three months of denture use.

Oral processing assessment:

TOMASS test were utilized to assess participants' oral processing during ingestion of solid food. For this study, a commercially available cracker (biscuit) will be used. Participants will be instructed to sit on a chair in upright position and to eat the biscuit comfortably and as quickly as possible. They also will be asked to say their name out loud as it indicates that they had finished the test. Using a video recorder the procedure will be recorded for further analysis.

The recorded videos were then analyzed using the Avidemux 2.6 program to measure the following:

• Swallowing threshold, which is the duration of chewing until the first swallow (determined by the moment of laryngeal elevation)
• The TOMASS test parameters:

• Number of bites: The number of discrete bites taken to finish the cracker
• Number of masticatory cycles: As each cyclical mandibular movement up-down
• Number of swallows: As each vertical movement of the thyroid cartilage
• Total ingestion time: The time taken to complete the ingestion of the cracker from the first bite to the last.

All participants were completely edentulous for at least 6 months,

• had no previous experience with removable prosthesis
• had Angel's class I maxillo-mandibular relation
• Willingness to comply with the study protocol and attending follow-up visits

Exclusion criteria

• Participants with temporo-mandibular joint disorders.
• head/neck injury, or with skeletal deformity.
• Inability to wear dentures for extended periods or intolerance to the study